Reflecting electrode forming method and liquid crystal display

ABSTRACT

The invention provides a method of forming a reflective electrode with a reduced number of manufacturing steps and a reduced cost, and provides a liquid crystal display device to which said method is applied. A resist coating is applied on a reflective electrode film ( 3 ). Then the resist coating is exposed to light and developed in such a way that the remaining portions ( 4 ) of the resist coating having a plurality of holes ( 4   a ) remain. Then the reflective electrode film ( 3 ) is dry-etched using the remaining portions ( 4 ) as etching masks. Such a dry etching of the reflective electrode film ( 3 ) using the remaining portions ( 4 ) as etching masks forms a reflective electrode ( 30 ) having a plurality of holes ( 30   a ) in each pixel. Further, since the thickness changing region ( 30   b ) in which a thickness changes continuously is provided in the periphery of each hole ( 30   a ), the reflective electrode ( 30 ) can have a desired reflective characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a reflective electrode and a liquid crystal display device comprising a reflective electrode formed using this method.

2. Description of Related Art

In a liquid crystal display device comprising reflective electrodes, those reflective electrodes are provided with recesses or projections so as to have a desired reflective characteristic.

It is required to form a photosensitive resin patterned into a predetermined form below the reflective electrodes for the purpose of providing reflective electrodes with recesses or projections, so that there is a problem of increasing the number of manufacturing steps and a manufacturing cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of forming a reflective electrode with a reduced number of manufacturing steps and a reduced manufacturing cost, and provide a liquid crystal display device to which this method is applied.

A method of forming a reflective electrode according to the present invention for achieving the object described above is a method of forming a plurality of reflective electrodes on a substrate, is characterized in that said method comprises the step of forming a first film on said substrate, said first film having a material of said reflective electrode and the step of patterning said first film in such a way that a portion of said first film corresponding to said reflective electrode remains, and that, in said patterning step, a thickness changing region in which a thickness changes continuously is formed in said portion of said first film corresponding to said reflective electrode.

In the method of forming a reflective electrode according to the present invention, a thickness changing region in which a thickness changes continuously is formed in the portion of the first film corresponding to each reflective electrode, so that the thickness changing region can be formed in each of the plurality of reflective electrodes. It is possible to provide the reflective electrode with a good reflective characteristic by forming the thickness changing region in each reflective electrode. Further, in the method of forming a reflective electrode according to the present invention, the thickness changing region is formed in the step of patterning the first film in such a way that the portion of the first film corresponding to each reflective electrode remains. Therefore, in the method of forming a reflective electrode according to the present invention, there is no need to additionally provide a step of forming only a thickness changing region in order to form the reflective electrode having a good reflective characteristic other than the step of patterning the first film in such a way that the portion of the first film corresponding to each reflective electrode remains, so that the reflective electrode having a desired diffusion characteristic can be formed without increasing the number of manufacturing steps.

A method of forming a reflective electrode according to the present invention is preferably characterized in that, in said patterning step, said thickness changing region is formed so as to have a slope whose inclination is greater than 0 degree and smaller than 10 degrees.

When the thickness changing region has the inclination angle described above, the reflective electrode can have a good reflective characteristic.

A method of forming a reflective electrode according to the present invention is preferably characterized in that, in said patterning step, said thickness changing region is formed in such a way that a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is equal to or greater than 1.5.

When the ratio is equal to or greater than 1.5, the inclination angle greater than 0 degree and smaller than 10 degrees can be easily provided in the thickness changing region.

A method of forming a reflective electrode according to the present invention is preferably characterized in that said patterning step comprises a first step of forming a photosensitive film on said first film, a second step of exposing said photosensitive film to light and developing it to pattern said photosensitive film into a form corresponding to a pattern of said plurality of reflective electrodes, a third step of baking said patterned photosensitive film, and a fourth step of dry-etching said first film using said baked photosensitive film as an etching mask.

By means of the dry-etching of the first film using the baked photosensitive film as an etching mask, the thickness changing region can be easily formed in each reflective electrode.

A method of forming a reflective electrode according to the present invention is preferably characterized in that each of a plurality of pixel regions is provided with a respective one of said reflective electrodes, that each of said reflective electrodes has a plurality of holes, and that, in said second step, said photosensitive film is patterned in such a way that a portion of said photosensitive film corresponding to a periphery of each of said plurality of reflective electrodes and a portion of said photosensitive film corresponding to each of said plurality of holes are removed.

By means of the patterning of the photosensitive film as described above, one reflective electrode having a plurality of holes can be formed in each of the plurality of pixel regions.

A method of forming a reflective electrode according to the present invention is preferably characterized in that each of a plurality of pixel regions is provided with at least two of said reflective electrodes, and that, in said second step, said photosensitive film is patterned in such a way that a portion of said photosensitive film corresponding to a periphery of each of said plurality of reflective electrodes is removed.

By means of the patterning of the photosensitive film as described above, a plurality of reflective electrodes can be formed in each of a plurality of pixel regions.

A method of forming a reflective electrode according to the present invention preferably comprises a step of forming a plurality of transparent electrode before said step of forming said first film.

By means of the forming of the transparent electrodes, a liquid crystal display can be constructed so as to operate in both a reflective mode and transparent mode.

A liquid crystal display device according to the present invention comprises a plurality of reflective electrodes on a substrate, characterised in that each of said plurality of reflective electrodes has a thickness changing region in which a thickness changes continuously.

The liquid crystal display device according to the present invention can be characterised in that each of a plurality of pixel regions is provided with one of said reflective electrodes, that each of said reflective electrodes has a plurality of holes, and that said thickness changing region is provided in a peripheral portion of each hole, wherein a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is preferably equal to or greater than 1.5.

The liquid crystal display device according to the present invention can be characterised in that each of a plurality of pixel regions is provided with at least two of said reflective electrodes, and that said thickness changing region is provided in a peripheral portion of each of said plurality of reflective electrodes, wherein a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is preferably equal to or greater than 1.5.

The liquid crystal display device according to the present invention is preferably characterised in that said thickness changing region has a slope whose inclination is greater than 0 degree and smaller than 10 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a liquid crystal display device of transflective type having a passive matrix structure which is one example of a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view of the device taken along a line I-I in FIG. 1.

FIG. 3 is a plan view of the substrate 1 on which the scanning electrodes 2 have been formed.

FIG. 4 is a cross-sectional view of the substrate 1 taken along a line II-II in FIG. 3.

FIG. 5 is a plan view of the substrate after the reflective electrode film 3 has been formed.

FIG. 6 is a cross-sectional view of the substrate taken along a line III-III in FIG. 5.

FIG. 7 is a plan view of the substrate after the resist coating has been exposed to light and developed.

FIG. 8 is a cross-sectional view of the substrate taken along a line IV-IV in FIG. 7.

FIG. 9 is a cross-sectional view of the substrate after the remaining portions 4 have been baked.

FIG. 10 is an enlarged view of a region Z shown in FIG. 9.

FIG. 11 is a plan view of the substrate after the reflective electrode film 3 has been dry-etched.

FIG. 12 is a cross-sectional view of the substrate taken along a line V-V in FIG. 11.

FIG. 13 is an enlarged view of a region Z shown in FIG. 12.

FIG. 14 is a plan view of the substrate which is provided with the underlayer below the reflective electrode.

FIG. 15 is a cross-sectional view the substrate taken along a line VI-VI in FIG. 14.

FIG. 16 is a plan view of the resist coating immediately after the resist coating is exposed to light and developed in such a way that remaining portions having different shape from FIG. 7 remain.

FIG. 17 is a cross-sectional view taken along a line VII-VII in FIG. 16.

FIG. 18 is a cross-sectional view of the substrate after the portions 40 of the resist coating are baked.

FIG. 19 is an enlarged view of a region Z shown in FIG. 18.

FIG. 20 is a cross-sectional view of the dry-etched reflective electrode film 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Hereinafter, an embodiment of the present invention will be described referring to a liquid crystal display device of transflective type. However, it is noted that the present invention is also applicable to, for example, a liquid crystal display device which dose not have a transparent function but have only a transparent function.

FIG. 1 is a plan view of a liquid crystal display device of transflective type having a passive matrix structure which is one example of a liquid crystal display device according to the present invention. FIG. 2 is a cross-sectional view of the device taken along a line I-I in FIG. 1.

This liquid crystal display device 100 comprises two substrates 1 and 50 which are opposed each other with a liquid crystal layer 60 (see FIG. 2) sandwiched therebetween. In FIG. 1, a portion of the substrate 50 is cut away in such a way that a portion of the substrate 1 is visible. In FIG. 2, electrodes and others formed on the substrates 1 and 50 are omitted. Scanning electrodes 2 extending in the x direction (see, for example, FIG. 3 described later) are formed on the substrate 1 and a reflective electrode 30 is formed on the scanning electrode 2 at an area corresponding to each of the pixel regions. Data electrodes 51 extending in the y direction are formed on the other substrate 50. A backlight 70 is provided at the back side of the substrate 1.

Hereinafter, it will be described that the method of manufacturing the substrate 1 on which the reflective electrodes 30 being the characteristic portion of this embodiment have been formed.

First, the scanning electrodes 2 are formed on the substrate 1 (see FIG. 3).

FIG. 3 is a plan view of the substrate 1 on which the scanning electrodes 2 have been formed. FIG. 4 is a cross-sectional view of the substrate 1 taken along a line II-II in FIG. 3.

The scanning electrodes 2 extending in the x direction are formed on the substrate 1. The scanning electrodes 2 can be formed by forming a light transmissive film (e.g., ITO film) on the substrate 1 and patterning the light transmissive film into a form that corresponds to each of the scanning electrodes 2. FIG. 3 shows only two scanning electrodes 2, but it is noted that a large number of scanning electrodes 2 are actually formed. After forming the scanning electrodes 2, a reflective electrode film 3 for forming the reflective electrode 30 is formed (see FIG. 5 and FIG. 6).

FIG. 5 is a plan view of the substrate after the reflective electrode film 3 has been formed. FIG. 6 is a cross-sectional view of the substrate taken along a line III-III in FIG. 5.

In this embodiment, the reflective electrode film 3 is formed by layering a metallic material having a high melting point (for example, Ti, Mo and others) and a metallic material (for example Al), but other materials may also be used. Moreover, the reflective electrode film 3 may also have a single-layer structure. After forming the reflective electrode film 3, the reflective electrode 30 (see FIG. 1) is formed by patterning the reflective electrode film 3. For the purpose of patterning the reflective electrode film 3, a resist coating is formed on this reflective electrode film 3 by applying a resist on the film 3 and this resist coating is exposed to light and developed (see FIG. 7 and FIG. 8).

FIG. 7 is a plan view of the substrate after the resist coating has been exposed to light and developed. FIG. 8 is a cross-sectional view of the substrate taken along a line IV-IV in FIG. 7.

In this embodiment, the resist coating is exposed to light and developed in such a way that the portions 4 of the resist coating which correspond to the respective pixel region remain. In FIGS. 7 and 8, the portions (hereinafter, referred to as “remaining portions”) 4 of the resist coating are shown by hatched lines. A plurality of holes 4 a for exposing the reflective electrode film 3 are formed in the remaining portions 4. After the resist coating is exposed to light and developed, the remaining portions 4 are baked (see FIG. 9).

FIG. 9 is a cross-sectional view of the substrate after the remaining portions 4 have been baked. FIG. 10 is an enlarged view of a region Z shown in FIG. 9.

Before the remaining portions 4 are baked (see FIG. 8), an inner wall surface 4 b of each hole 4 a extends vertically with respect to the surface of the substrate 1. However, by means of the baking of the remaining portions 4, the remaining portions 4 melt, so that the shape of the inner wall surface 4 b is changed to a roundish shape as shown in FIG. 10. As a result of changing the shape of this inner wall 4 b, a thickness of a periphery 4 d of the hole 4 a increases continuously from the inner wall 4 b toward a top surface 4 c of the remaining portion 4. After the remaining portions 4 are baked, the reflective electrode film 3 is dry-etched using the remaining portions 4 as etching masks (see FIG. 11 and FIG. 12).

FIG. 11 is a plan view of the substrate after the reflective electrode film 3 has been dry-etched. FIG. 12 is a cross-sectional view of the substrate taken along a line V-V in FIG. 11.

By means of the dry-etching of the reflective electrode film 3, portions of the reflective electrode film 3 which are covered with the remaining portions 4 (hereinafter, referred to as “covered portions”) remain and portions of the reflective electrode film 3 which surround the covered portions are removed. Therefore, the reflective electrode 30 is formed below each of the remaining portions 4. For the etching gas, for example, BCl₃/Cl₂ can be used. In FIG. 11, the remaining portion 4 at the top left is partially cut away, so that a part of the reflective electrode 30 formed below the remaining portion 4 at the top left is visible. By means of the dry-etching of the reflective electrode film 30, a large number of holes 30 a for exposing the scanning electrode 2 can be formed in each reflective electrode 30 since each of the remaining portions 4 has a large number of holes 4 a. Formation of the holes 30 a in the reflective electrode 30 allows light emitted from the backlight 70 (see FIG. 2) to enter a liquid crystal layer 60 (see FIG. 2) through the holes 30 a of the reflective electrode 30, so that the liquid crystal display device 100 (see FIG. 1) can be used in a transparent mode. Furthermore, a film thickness changing region 30 b whose film thickness changes continuously is formed in the periphery of each hole 30 a by forming the holes 30 a in the reflective electrode 30. Hereinafter, it will be described that how this film thickness changing region 30 b is formed with reference to FIG. 13.

FIG. 13 is an enlarged view of a region Z shown in FIG. 12.

In FIG. 13, the reflective electrode film 3 and the remaining portion 4 before dry-etching are shown by dashed lines, and the reflective electrode 30 (that is, the dry-etched reflective electrode film 3) and the remaining portion 4′ after dry-etching are shown by solid lines.

Before the dry-etching is started, a first portion 3 a of the reflective electrode film 3 is not covered with the remaining portion 4. Therefore, the dry etching cause the first portion 3 a of the reflective electrode film 3 to be removed. Furthermore, the dry etching cause the remaining portion 4 to be reduced, so that the remaining portion 4 is finally changed into the remaining portion 4′ having a shape shown by a solid line. Therefore, a second portion 3 b of the reflective electrode film 3 is covered with the remaining portion 4 before the dry-etching is started, but the second portion 3 b is exposed during the dry etching, so that not only the first portion 3 a but also the second portion 3 b are etched. However, it is noted that the periphery 4 d of the hole 4 a formed in the remaining portion 4 shows a distribution of film thickness which increases continuously from the inner wall surface 4 b toward the top surface 4 c of the remaining portion 4. The times between the start of etching and the exposure of the second portion 3 b are different among the different regions within the second portion 3 b because of the difference of the film thickness within the periphery 4 d. Because the times of exposure are different, an etching depth E of the second portion 3 b changes continuously within the second portion 3 b.

Since the reflective electrode film 3 is etched by means of the process described above, a thickness changing region 30 b whose thickness changes continuously is formed in the periphery (shaded area in FIG. 13) of the hole. 30 a formed in the reflective electrode 30. An inclination angle θ at each position of a surface 30 c of the thickness changing region 30 b is preferably within a range which is greater than 0 degree and smaller than 10 degrees. When the inclination angle θ is within the range described above, the reflective electrode 30 can have a good reflective characteristic. It is not required that the inclination angle θ is within the range greater than 0 degree and smaller than 10 degrees over the whole surface 30 c of the thickness changing region 30 b. However, the inclination angle θ is preferably within the range greater than 0 degree and smaller than 10 degrees over more than half of the surface 30 c of the thickness changing region 30 b to secure a good reflective characteristic. For this purpose, it is considered that, for example, the reflective electrode film 3 is etched until a ratio R of a maximum value t_(max) of thickness of the thickness changing region 30 b to a width w of the thickness changing region 30 b becomes equal to or greater than R=1.5. This allows the inclination θ to be within the range greater than 0 degree and smaller than 10 degrees over more than half of the surface 30 c of the thickness changing region 30 b.

After the etching of the reflective electrode film 3 is completed, the remaining portion 4 is removed.

The reflective electrode 30 is formed by means of the process described above.

In this embodiment, since the reflective electrode 30 has the thickness changing region 30 b, this reflective electrode 30 can have a good reflective characteristic. In contrast, in order that the reflective electrode 30 may have a good reflective characteristic, it is considered to form an underlayer below the reflective electrode 30 for providing the reflective electrode 30 with a good reflective characteristic, instead of forming the thickness changing region 30 b in the reflective electrode 30. However, the method of forming the underlayer below the reflective electrode 30 has the following disadvantage. This disadvantage will be described with reference to FIGS. 14 and 15.

FIG. 14 is a plan view of the substrate which is provided with the underlayer below the reflective electrode. FIG. 15 is a cross-sectional view the substrate taken along a line VI-VI in FIG. 14.

In the reflective electrode 400 (shown by shaded areas), a window 400 a for passing through a light from the backlight is formed. Below the reflective electrode 400, an underlayer 50 for providing the reflective electrode 400 with projections and recesses is formed. Forming the underlayer 50 below the reflective electrode 400 makes the reflective electrode 400 have a desired reflective characteristic. However, in the method shown in FIGS. 14 and 15, in order that the reflective electrode 400 may have projections and depressions, there is a need to carry out not only a patterning step for forming the reflective electrode 400 but also a step of forming the underlayer 50 for providing the reflective electrode 400 with projections and depressions.

In contrast, according to this embodiment, the thickness changing region 30 b to be formed in the reflective electrode 30 is formed while the reflective electrode film 3 is being patterned. Thus, this embodiment can reduce the number of manufacturing steps and a manufacturing cost compared with the method shown in FIGS. 14 and 15.

In the embodiment, in order that the reflective electrode 30 may have the thickness changing region 30 b, the resist coating is exposed to light and developed in such a way that the remaining portions 4 each having many holes 4 a remain as shown in FIG. 7. However, there is not always a need to expose to light and develop the resist coating in such a way that the remaining portions 4 each having many holes 4 a remain. The resist coating may also be exposed to light and developed in such a way that remaining portions having different shape from FIG. 7 remain. An example where remaining portions having different shape from FIG. 7 remain will be described below.

FIG. 16 is a plan view of the resist coating immediately after the resist coating is exposed to light and developed in such a way that remaining portions having different shape from FIG. 7 remain. FIG. 17 is a cross-sectional view taken along a line VII-VII in FIG. 16.

In FIG. 16 and FIG. 17, the resist coating is exposed to light and developed in such a way that many remaining portions 40 having almost round shape remain in an area corresponding to each pixel region P. In FIG. 16 and FIG. 17, the areas where the remaining portions 40 exist are shown by hatched lines. After the resist coating is exposed to light and developed, the remaining portions 40 of the resist coating are baked (see FIG. 18 and FIG. 19).

FIG. 18 is a cross-sectional view of the substrate after the portions 40 of the resist coating are baked. FIG. 19 is an enlarged view of a region Z shown in FIG. 18.

Before the remaining portions 40 of the resist coating are baked (see FIG. 17), side surface 40 a of each remaining portions 40 extends vertically with respect to the surface of the substrate 1. However, through the post-baking of the remaining portions 40 of the resist coating, the remaining portions 40 melt, so that the shape of the side surface 40 a is changed to a roundish shape as shown in FIG. 19. As a result of changing the shape of the side surface 40 a, a thickness of an outer edge 40 c of the remaining portion 40 increases continuously from the side surface 40 a toward a top surface 40 b of the remaining portion 40. The reflective electrode film 3 is dry-etched using the remaining portions 40 as etching masks (see FIG. 20).

FIG. 20 is a cross-sectional view of the dry-etched reflective electrode film 3.

The dry-etching of the reflective electrode film 3 using the remaining portions 40 as etching masks causes the reflective electrode 31 to be formed below each of the remaining portions 40. Therefore, a thickness changing region 31 a whose thickness changes continuously is formed in an outer edge of the reflective electrode 31 in the same way as described with reference to FIG. 13. Thus, this reflective electrode 31 can have a good reflective characteristic as in the case of the reflective electrode 30 (see FIG. 11).

In the embodiment, the liquid crystal display device 100 in which a passive matrix scheme is adopted is shown, but the present invention is also applicable to a liquid crystal display device in which for example an active matrix scheme using a switching element such as TFT is adopted.

The present invention provides a method of forming a reflective electrode with a reduced number of manufacturing steps and a reduced manufacturing cost, and provide a liquid crystal display device to which this method is applied. 

1. A method of forming a plurality of reflective electrodes on a substrate, wherein said method comprises the steps of: forming a first film on said substrate, said first film having a material of said reflective electrode; and patterning said first film in such a way that a portion of said first film corresponding to said reflective electrode remains; and wherein, in said patterning step, a thickness changing region in which a thickness changes continuously is formed in said portion of said first film corresponding to said reflective electrode.
 2. A method as claimed in claim 1, wherein, in said patterning step, said thickness changing region is formed so as to have a slope whose inclination is greater than 0 degree and smaller than 10 degrees.
 3. A method as claimed in claim 1, wherein, in said patterning step, said thickness changing region is formed in such a way that a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is equal to or greater than 1.5.
 4. A method as claimed in any one of claim 1, wherein said patterning step comprises: a first step of forming a photosensitive film on said first film; a second step of exposing said photosensitive film to light and developing it to pattern said photosensitive film into a form corresponding to a pattern of said plurality of reflective electrodes; a third step of baking said patterned photosensitive film; and a fourth step of dry-etching said first film using said baked photosensitive film as an etching mask.
 5. A Method as claimed in claim 4, wherein each of a plurality of pixel regions is provided with a respective one of said reflective electrodes, wherein each of said reflective electrodes has a plurality of holes, and wherein, in said second step, said photosensitive film is patterned in such a way that a portion of said photosensitive film corresponding to a periphery of each of said plurality of reflective electrodes and a portion of said photosensitive film corresponding to each of said plurality of holes are removed.
 6. A method as claimed in claim 4, wherein each of a plurality of pixel regions is provided with at least two of said reflective electrodes, and wherein, in said second step, said photosensitive film is patterned in such a way that a portion of said photosensitive film corresponding to a periphery of each of said plurality of reflective electrodes is removed.
 7. A method as claimed in claim 1, wherein said method comprises a step of forming a plurality of transparent electrode before said step of forming said first film.
 8. A liquid crystal display device comprising a plurality of reflective electrodes having a thickness changing region in which a thickness changes continuously.
 9. A liquid crystal display device as claimed in claim 8, wherein each of a plurality of pixel regions is provided with one of said reflective electrodes, wherein each of said reflective electrodes has a plurality of holes, and wherein said thickness changing region is provided in a peripheray of each hole.
 10. A liquid crystal display device as claimed in claim 9, wherein a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is equal to or greater than 1.5.
 11. A liquid crystal display device as claimed in claim 8, wherein electrodes, and wherein said thickness changing region is provided in an outer edge of each of said plurality of reflective electrodes.
 12. A liquid crystal display device as claimed in claim 11, wherein a ratio of a width of said thickness changing region to a maximum value of thickness of said thickness changing region is equal to or greater than 1.5.
 13. A liquid crystal display device as claimed in claim 8, wherein said thickness changing region has a slope whose inclination is greater than 0 degree and smaller than 10 degrees.
 14. A liquid crystal display device as claimed in claim 8, wherein a transparent electrode is formed below the said reflective electrode. 